The pipette, or metering syringe, of the invention as will be described herein, is useful in conjunction with a blood clot timing mechanism of the type described, for example, in copending application Ser. No. .[.730,832.]. .Iadd.738,382. .Iaddend.However, it will become evident as the description proceeds that the metering syringe of the invention has general utility whenever a precisely metered amount of a liquid is to be introduced into a receptacle, or the like, for test or other purposes.
The blood clot timing system described in the aforesaid copending application, in one of its aspects, is capable of detecting clotting in a blood or plasma sample, this being achieved by the application in special equipment of a test for determining the prothrombin time. The aforesaid test involves the addition of a measured amount of the patient's blood, or plasma, to a reagent, such as thromboplastin; and the subsequent addition of a measured amount of calcium chloride, or other source of soluble calcium ions, to the solution. As described in the copending application, a timer in the equipment is started at the precise time the calcium chloride is added to the solution.
The metering syringe of the present invention is particularly suited for use in conjunction with the test described in the preceding paragraph. The syringe may be equipped with a replaceable, disposable tip so that it may be used to add different blood samples to different receptacles of reagent, and also to add the calcium chloride, all without fear of contamination. For each operation, the previous tip is discarded and replaced by a new sterile tip.
The improved metering syringe of the invention is also equipped with an improved simplified purging mechanism, which is effective to provide an additional discharge stroke as compared with the intake stroke. This additional discharge stroke enables the last drop of the liquid, which was drawn into the instrument by the intake stroke, to be discharged during the discharge stroke. In this manner, the exact quality of liquid drawn into the syringe instrument is discharged, and also the instrument is completely purged.
The improved syringe to be described herein is also equipped with electrical contacts which are closed at the end of the discharge stroke. These contacts are useful, for example, in conjunction with the equipment of the copending application to control the commencement of the timer the instant the calcium chloride is added to the solution.
The invention provides, therefore, an improved syringe type of instrument which is capable of introducing a precisely measured amount of liquid into a receptacle, and which includes a purge control so that all the liquid drawn into the instrument is discharged during the discharge stroke. The instrument to be described is extremely simple in its construction, and yet it is precise and accurate in its operation. The instrument to be described, moreover, is capable of closing an electric circuit at the termination of its discharge stroke, for reasons such as mentioned above.
The instrument of the invention finds particular utility in blood tests, such as referred to above. This is because precision is an essential requirement in such tests, as is freedom from contamination. However, it will become evident as the description proceeds, and as mentioned previously herein, that the instrument of the invention has general utility.